In order to make informed HIV prevention resource allocation decisions, public health decision makers require detailed information about the cost and cost-effectiveness of various HIV prevention interventions. The Cost-Effectiveness Studies Core supports scientific research into the cost, economic efficiency, and effectiveness of HIV primary prevention interventions, related behavioral modification programs, and intervention dissemination activities. The Core provides consultations to CAIR investigators regarding the feasibility of conducting economic efficiency or modeling studies of proposed, ongoing, or completed HIV prevention interventions, including dissemination-based interventions. The Core identifies appropriate economic evaluation or mathematical modeling techniques for assessing the cost-effectiveness of the intervention and collaborates with intervention researchers on the design of suitable behavioral measurement and cost data collection instruments to support the conduct of prospective or retrospective economic evaluation research and modeling studies. Core scientists take a lead role in performing these analyses, in collaboration with other CAIR investigators. As appropriate to the specific needs of the intervention project, support activities undertaken by the Core may include prospective data collection during the course of an ongoing intervention trial, retrospective data collection after a trial is complete, mathematical modeling to quantify intervention effectiveness in epidemiologically-meaningful units (e.g., HIV infections averted or expected number of secondary infections), and/or cost-effectiveness, cost-utility, or threshold analyses to determine the overall economic efficiency of HIV prevention interventions. The recent addition to the Core of Carol Galletly, J.D., Ph.D., a behavioral scientist and legal scholar whose work focuses on the intersection of HIV prevention and law, has allowed the Cost-Effectiveness Studies Core to expand its policy dimension to encompass the relationship between HIV-related legal statutes, HIV risk behaviors, and HIV prevention, and to better address ethical issues in social science research. Reflecting this new function, the Core now provides consultation to CMR scientists on compliance with applicable law and policy governing the ethical conduct of research involving human participants.